This section provides information helpful in understanding the invention but that is not necessarily prior art.
Binder materials having carbamate groups have been used in thermosetting coating composition, for instance automotive clearcoat compositions. Such binder materials may be cured with relatively low viscosity aminoplast resins, which allow the coating formulations to have higher solids, to form cured coating with excellent durability, including resistance to scratching, marring, and weathering degradation. Carbamate groups may be introduced onto a binder material by reaction of a hydroxyl-functional material with an alkyl carbamate, for example methyl carbamate or butyl carbamate, through what is referred to as “transcarbamation” or “transcarbamoylation.”
Tin-based catalysts have been the preferred catalysts for performing transcarbamation due to high yields. However, regulation of tin catalysts, particularly in Europe, makes it desirable to not use tin catalysts. Moreover, using tin catalysts tends to result in an unwanted increase in molecular weight of resins from catalysis of side reactions. Finally, an increase in yellowing has been noted when tin catalysts are used.